One thing that flexible circuits and rigid printed circuit boards(Rigid Flex PCB) have in common is that they both allow repeatable connections. Conductor routings in a flexible circuit are determined just like a rigid PC board by a single artwork, rather than by individual wirings.
Flexible circuits(Flex PCB) also allow extra-fine lines, as low as 2 mils on 4-mil centers, allowing high -density device population and reduced circuit size and weight.
But flexible circuits have one important advantage over rigid PC boards in that they give designers a third dimension with which to work. Flexible circuits can bend and shape around two or more planes during installation. They can solve space and weight problems by replacing several bulky boards with a single thin one. While in use, flexible circuits can also bend and flex up to 500 million times without a failure. This is something a rigid PC board simply cannot do.